Fake finger determination apparatus and fake finger determination method

ABSTRACT

The present invention improves an accuracy to discern a fake finger created by attaching a transparent thin film to the surface of a finger. The present invention has: a mounting surface that has a mounting area to mount an authentication target that is an object of fingerprint authentication; a transparent plate that is provided on mounting surface and defines a range of an image used for determining the authenticity of the authentication target; a light source that allows light to directly enter the authentication target mounted on the mounting area, not by way of the transparent plate; and an imaging device that images the authentication target mounted on the mounting area, by way of a the transparent plate, wherein a light emitting surface for emitting light of the light source to outside is disposed on the same plane as the mounting surface.

The present invention relates to a fake finger determination apparatusand a fake finger determination method.

BACKGROUND ART

Fingerprint authentication is receiving attention lately as oneauthentication method to identify an individual. A fingerprint dependson the individual, and does not change over time. Therefore fingerprintauthentication should have higher reliability than passwordauthentication, which is commonly used today. On the other hand, in thecase of fingerprint authentication, it is necessary to prevent theillegal act of pretending to be the actual individual by using a fakefinger with a forged fingerprint of the actual individual. As atechnology to prevent such illegal acts, Patent Documents 1 and 2disclose a technology to detect a fake finger based on the color on thesurface of a finger onto which light is irradiated. Patent Document 3discloses a technology to detect a fake finger by irradiating light ontoa finger from a location above the finger, and photographing a lighttransmitting through the finger. Patent Document 4 discloses atechnology to detect a fake finger, created by attaching a thin filmwith a forged fingerprint to the surface of a finger, by irradiating alight onto the finger from the side, and using an obtained diffusionpattern of the light transmitted through the finger for identification.

[Patent Document 1] Patent Publication JP-A-2003-50993

[Patent Document 2] Japanese Patent Publication No. 2637253

[Patent Document 3] Patent Publication JP-A-H9-134419

[Patent Document 4] Patent Publication JP-A-2007-249296

In the case of the technology to detect a fake finger based on the colorof the surface of the finger disclosed in Patent Documents 1 and 2, andthe technology detect a fake finger by irradiating light onto the fingerfrom an area above the finger disclosed in Patent Document 3, a fakefinger created by attaching a transparent thin film with a forgedfingerprint to a finger cannot be detected. This is because, accordingto Patent Documents 1 and 2, it is difficult to distinguish between thecolor of the surface of the fake finger on which the transparent thinfilm is attached and that of real skin color. In the case of PatentDocument 3, the attenuation factor of the light that transmits throughthe transparent thin film is low, and it is difficult to distinguish thelight that transmitted through the finger and the thin film from thelight that transmitted only through the finger.

In the case of the technology to detect a fake finger by irradiatinglight onto the finger from the side disclosed in Patent Document 4,light may not be irradiated directly onto the thin film attached to thesurface of the finger. In this case, the fake finger cannot be detected,just like Patent Document 3. For example, if the finger is pressedagainst a fingerprint sensor surface, it is possible that a part of thefinger could cover an area around the thin film, and the light that issupposed to be irradiated onto the thin film could be blocked by part ofthe finger. In this case, the light is not irradiated directly onto thethin film, and the same state as Patent Document 3 occurs. As a result,it becomes difficult to distinguish the light that transmitted throughthe finger and the thin film from the light that transmitted onlythrough the finger.

SUMMARY

With the foregoing in view, it is an object of the present invention toprovide a fake finger determination apparatus and a fake fingerdetermination method that can improve an accuracy to discern a fakefinger created by attaching a transparent (the meaning of “transparent”in this description includes “translucent”) thin film to the surface ofthe finger.

A fake finger determination apparatus of the present invention includes:a mounting surface that has a mounting area to mount an authenticationtarget that is an object of fingerprint authentication; an imaging unitthat is provided on the mounting surface and images the authenticationtarget mounted on the mounting area by way of an image capturing areathat defines a range of an image to be captured; and one or a pluralityof light sources that allow light to directly enter the authenticationtarget mounted on the mounting area not by way of the image capturingarea, wherein a light emitting surface for emitting the light of thelight sources to outside is disposed on the same plane as the mountingsurface.

A fake finger determination method of the present invention includessteps of: mounting an authentication target that is an object offingerprint authentication on a mounting surface that has a mountingarea to mount the authentication target; allowing light from a lightsource to directly enter the authentication target mounted on themounting area, not by way of an image capturing area that is provided onthe mounting surface and defines a range of an image to be captured; andimaging the authentication target mounted on the mounting surface byusing the imaging unit, by way of the image capturing area, wherein alight emitting surface for emitting the light of the light sources tooutside is disposed on the same plane as the mounting surface.

According to the present invention, an accuracy to discern a fake fingercreated by attaching a transparent thin film to the surface of thefinger can be improved.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view depicting a fake finger determination apparatusaccording to the first embodiment viewed from directly above;

FIG. 2 is a cross-sectional view sectioned at II-II in FIG. 1;

FIG. 3A is a graph depicting a relationship between the distance fromthe light source and the brightness value of the transmitted light imageof a human finger, and

FIG. 3B is a schematic diagram of the distance from the light sourceaccording to the abscissa of the graph in FIG. 3A;

FIG. 4 is a graph depicting the upper limit and the lower limit of thebrightness value of the transmitted light image shown in FIG. 3A;

FIG. 5 is a graph depicting a relationship between the distance from thelight source and the brightness value of the transmitted light image inthe case of imaging a fake finger created by attaching a transparentfilm to the surface of the finger;

FIG. 6 is a graph depicting a relationship between the distance from thelight source and the brightness value of the transmitted light image inthe case of imaging a fake finger created by attaching an opaque film tothe surface of the finger;

FIG. 7 is a diagram depicting an arrangement of the light sourcesaccording to a variant form;

FIG. 8 is a diagram depicting an arrangement of the light sourcesaccording to a variant form;

FIG. 9 is a graph depicting a method for calculating an attenuationfactor according to the second embodiment;

FIG. 10 is a plan view depicting a fake finger determination apparatusaccording to the third embodiment viewed from directly above;

FIG. 11 is a cross-sectional view sectioned at XI-XI in FIG. 10;

FIG. 12 is a diagram depicting a first mounting area;

FIG. 13 is a diagram depicting a second mounting area;

FIG. 14 is a diagram depicting a method for combining a plurality oftransmitted light images; and

FIG. 15 is a diagram depicting a configuration of a fake fingerdetermination apparatus according to a variant form.

DETAILED DESCRIPTION

Preferred embodiments of a fake finger determination apparatus and afake finger determination method according to the present invention willnow be described with reference to the accompanying drawings.

First Embodiment

A configuration of a fake finger apparatus according to the firstembodiment will be described first with reference to FIG. 1 and FIG. 2.FIG. 1 is a plan view depicting the fake finger determination apparatusviewed from directly above. FIG. 2 is a cross-sectional view sectionedat II-II in FIG. 1.

The fake finger determination apparatus 1 is an apparatus to determinewhether or not an authentication target T, to be an object of thefingerprint authentication, is a fake finger. An authentication targetT, that is a finger F on which surface a thin film M is attached, ismounted on the fake finger determination apparatus 1 shown in FIG. 2. Afingerprint of someone else is copied onto this thin film M. In thiscase, the fake finger determination apparatus 1 determines that theauthentication target T is a fake finger. If only a finger F is mountedon the fake finger determination apparatus 1 as the authenticationtarget T, on the other hand, the fake finger determination unit 1determines that the authentication target T is not a fake finger, but isa human finger. The configuration of the fake finger determinationapparatus 1 will now be described in concrete terms.

As FIG. 1 and FIG. 2 illustrate, the fake finger determination apparatus1 has an enclosure 10, a transparent plate 20, a light source 30, animaging device (imaging unit) 40 and a controller 50. In the descriptionherein below, the side where the transparent plate 20 is disposed is theupper side of the enclosure 10. The surface of the enclosure 10 wherethe transparent plate 20 is disposed, that is the top face of theenclosure 10, is the mounting surface to mount the authentication targetT.

Each composing element of the fake finger determination apparatus 1,that is the enclosure 10, the transparent plate 20, the light source 30,the imaging device 40 and the controller 50, is basically the same as anenclosure, a transparent plate, a light source, an imaging device and acontroller of a conventional fingerprint authentication apparatus. Adifference from a conventional fingerprint authentication apparatus,however, is in the arrangement of the light source 30 (including thelight emitting surface) and the controller 50 that has a function todetermine the authenticity of the authentication target.

The transparent plate 20 and the light source 30 are disposed so thatthe respective top faces are located on the same plane as the mountingsurface. A mounting area P, to mount the authentication target T, iscreated on the top faces of the transparent plate 20 and the lightsource 30.

The imaging device 40 is disposed below the transparent plate 20. Theimage device 40 captures an image from inside the enclosure 10 in thedirection of the transparent plate 20. In other words, the imagingdevice 40 images the authentication target T mounted on the mountingarea P by way of the transparent plate 20.

Out of an image captured by the imaging device 40, the portion insidethe frame of the transparent plate 20 is an image used for determiningthe authenticity of the authentication target T mounted on the mountingarea P. In other words, the transparent plate 20 defines thedetermination target area (image capturing area) to determine whetherthe authentication target T is a fake finger.

The light source 30 is disposed so that the top face (light emittingsurface) thereof is located on the same plane as the mounting surface.Thereby the light can be irradiated onto the authentication target T,mounted on the mounting area P, from the bottom of the authenticationtarget. If a thin film M is attached to the surface of a human finger F,the probability that the light will directly enter the thin film M canbe increased because of this arrangement. According to this embodiment,the light emitting surface to emit the light of the light source tooutside the fake finger determination apparatus is created by the topface of the light source 30.

It is preferable that the light emitting surface of the light source 30is disposed in a position adjacent to the transparent plate 20. Becauseas the light emitting surface of the light source 30 becomes closer tothe transparent plate 20, the probability that the light will directlyenter the thin film M attached to the surface of the human finger F canbe increased. The reflected light from the authentication target Thowever must not be included in the transmitted light image. If thereflected light from the authentication target T is included in thetransmitted light image, the brightness value of the transmitted lightimage increases, and the later mentioned accuracy, to determine a fakefinger by the determining unit 51, drops. To prevent inclusion of thereflected light from the authentication target T in the transmittedlight image, the light source 30 should be disposed as follows.

The light source 30 is disposed so that the light emitting surfacethereof is located in the position where the light can directly enterthe authentication target T mounted on the mounting area P, not by wayof the transparent plate 20 which is a determination target area.Thereby the imaging device 40 can capture a transmitted light imagewhich includes the light transmitted through the authentication target Tmounted on the mounting area P, and does not include the light reflectedon the surface of the authentication target T.

The controller 50 controls the entire fake finger determinationapparatus 1 by executing various control processings. The controller 50has a determining unit 51, for example.

The determining unit 51 determines the authenticity of theauthentication target T using the brightness value of the image capturedby the imaging device 40. In concrete terms, the determining unit 51determines the authenticity of the authentication target depending onwhether the brightness value of a predetermined pixel, included in thetransmitted light image captured by the imaging device 40, is within apredetermined range.

For the predetermined pixel, a pixel located in a position somewhatdistant from the light source 30 can be set, for example. This isbecause the light irradiated from the light source 30 onto a fingergradually attenuates inside the finger, and if a pixel close to thelight source 30 is set for the predetermined pixel, attenuation of thelight is so little that it is difficult to determine the authenticity ofthe authentication target T. At least one pixel can be set as thepredetermined pixel, but it is preferable to set a plurality of pixelswith a predetermined interval from a location close to the light source30 to a location distant from the light source 30. If a plurality ofpixels are set, brightness values according to the attenuation state ofthe light inside the finger can be obtained if the authentication targetT is a human finger, and determination accuracy can be further improved.

For the predetermined range, a range of brightness values which a humanfinger imaged as the authentication target T could have, for example,can be used. Here it is known that the light transmittance (attenuationfactor) in the human skin is confined to within a specific rangedepending on the wavelength of the light. If light is irradiated ontothe surface of the skin and the light that transmits through the skin isimaged, the brightness value of the transmitted light image tends tobecome smaller as the distance from the light source increases. Thebrightness value of the transmitted light image of a human finger willnow be described with reference to FIG. 3 and FIG. 4.

The brightness value of the transmitted light image in the case ofimaging a human finger as the authentication target will be describedwith reference to FIG. 3. FIG. 3A is a graph depicting a relationshipbetween the distance from the light source and the brightness value ofthe transmitted light image of a human finger. The abscissa of FIG. 3Aindicates a distance from the light source, and the ordinate indicates abrightness value of the transmitted light image. FIG. 3B is a schematicdiagram depicting the distance from the light source according to theabscissa of the graph in FIG. 3A. As FIG. 3A and FIG. 3B show, thebrightness value of the transmitted light image increases as thedistance from the light source 30 decreases, and the brightness value ofthe transmitted light image decreases as the distance from the lightsource 30 increases. This is because the light irradiated onto thesurface of the finger gradually attenuates inside the finger.

FIG. 4 is a graph depicting the upper limit and the lower limit of thebrightness value of the transmitted light image shown in FIG. 3A. Inother words, FIG. 4 is a graph depicting a range of brightness valueswhich a human finger, imaged as the authentication target, could have.In this case, the determining unit 51 determines that the authenticationtarget is a human finger if the brightness value of a pixel located atpoint A of the transmitted light image is in the range of “a2” to “a1”,and the brightness value of a pixel located at point B of thetransmitted light image is in the range of “b2” to “b1”.

A number of pixels used for determination (hereafter called “pixels fordetermination”) can be freely set. If a plurality of pixels fordetermination is set, the determining unit 51 can determine that theauthentication target is a human finger when the brightness values ofall the pixels for determination are within a predetermined range. Itmay be determined that the authentication target is a human finger whena number of pixels for determination, having a brightness value which iswithin a predetermined range, is a predetermined value or more.

A brightness value of a transmitted light image when a fake fingercreated by attaching a thin film to the surface of a human finger isimaged, on the other hand, is outside the predetermined range. Thebrightness value of the transmitted light image of a fake finger createdby attaching a thin film to the surface of a human finger will bedescribed with reference to FIG. 5 and FIG. 6.

FIG. 5 is a graphic depicting a relationship between the distance fromthe light source and the brightness value of the transmitted light imagein the case of imaging a fake finger created by attaching a transparentfilm to the surface of the finger. As FIG. 5 shows, the brightness valueof the pixel located at point A is higher than “a1”, and the brightnessvalue of the pixel located at point B is higher than “b1”. This isbecause an image of the light transmitted only through the transparentfilm (see the dotted arrow L in FIG. 2) is included in the transmittedlight image. The transmittance of the transparent film is higher thanthe transmittance of the human finger, therefore the transmitted lightimage of the transparent film becomes brighter than the transmittedlight image of the human finger.

FIG. 6 is a graph depicting a relationship between the distance from thelight source and the brightness value of the transmitted light image inthe case of imaging a fake finger created by attaching an opaque film tothe surface of the finger. As FIG. 6 shows, the brightness value of thepixel located at point A is lower than “a2”, and the brightness value ofthe pixel located at point B is lower than “b2”. This is because animage of the light transmitted through the opaque film is included inthe transmitted light image. The transmittance of the opaque film islower than the transmittance of the human finger, therefore thetransmitted light image of the opaque film becomes darker than thetransmitted light image of the human finger.

As described above, according to the fake finger determination apparatus1 of the first embodiment, the authenticity of the authentication targetcan be determined depending on whether a brightness value of apredetermined pixel included in the transmitted light image captured bythe imaging device 40 is within a range of brightness values, which ahuman finger imaged as the authentication target T, could have.

According to the fake finger determination apparatus 1 of the firstembodiment, the light source 30 can be disposed so that the top facethereof is located on the same plane as the mounting surface, and can bedisposed in a location so that the light can directly enter theauthentication target T, not by way of the transparent plate 20. Therebylight can be irradiated onto the authentication target T mounted on themounting area P, from the bottom of the authentication target T. If thehuman finger on which surface a thin film is attached is mounted on themounting area P, a probability that the top face of the light source 30,which is located on the same plane as the mounting surface, will contactthe thin film increases, and as a result, a probability that the lightwill directly enter the thin film can be increased. Hence the accuracyto discern a fake finger created by attaching a thin film to a surfaceof a human finger can be improved.

Furthermore the light source 30 is disposed adjacent to the transparentplate 20, thereby a probability that the light will directly enter thethin film attached to the surface of the human finger can be furtherincreased.

According to the above described first embodiment, one light source 30is disposed on one side of the transparent plate 20 (a determinationtarget area), but the arrangement of the light source is not limited tothis. For example, one light source 30 may be disposed on both sides ofthe transparent plate 20 (determination target area) respectively, asshown in FIG. 7. Or a plurality of light sources 30 may be disposed onboth sides of the transparent plate 20 (determination target area)respectively, as shown in FIG. 8. In this case, the quantity of lightthat transmits through the skin can be increased by arranging the lightsources 30 so as to cover the determination target area.

According to the above described first embodiment, the authenticity ofthe authentication target is determined using a brightness value of apredetermined pixel included in the transmitted light image captured bythe imaging device 40, but the means of obtaining the brightness of thepredetermined pixel is not limited to the imaging device 40. Forexample, instead of the imaging device 40, an illuminance sensor(imaging unit) for detecting brightness of a predetermined pixel may bedisposed for each predetermined pixel, and the authenticity of theauthentication target may be determined using the brightness of thepredetermined pixel detected by this illuminance sensor.

For the wavelength of the light source 30, a wavelength in the 700 nm to1200 nm range, which is called the “therapeutic window”, may be used. Ifa wavelength in the 700 nm to 1200 nm range is used, the quantity oflight that transmits through the skin can be increased, therefore whiledetermining the authenticity of the authentication target as mentionedabove, a skin pattern to be used for fingerprint authentication can beobtained at the same time. In the case of obtaining a skin pattern atthe same time, it is preferable that the light sources 30 are arrangedas illustrated in FIG. 8, for example. By arranging the light sources soas to cover the entire determination target area, more light cantransmit through the finger, and accuracy to obtain the skin pattern canbe improved.

The above mentioned light source 30 of the first embodiment is disposed,so that the top face thereof is located on the same plane as themounting surface, but the position of the light source 30 is not limitedto this. It is required to dispose the light source 30 in a position sothat light can be irradiated onto the authentication target T mounted onthe mounting area P from the bottom of the authentication target T. As aconcrete example, the light source 30 is disposed in a location belowthe mounting area P, and the light emitting surface, to emit the lightof the light source to outside the fake finger determination apparatus,is separately disposed so as to be located on the same plane as themounting surface. The light emitting surface in this case can bedisposed as follows. For example, the light source 30 is surrounded by ashielding wall to create an optical path, this optical path is extended,and the end face of this optical path becomes a light emitting surface.

Second Embodiment

A second embodiment of the present invention will now be described.According to the fake finger determination apparatus of the secondembodiment, the authenticity of the authentication target is determinedbased on the degree of attenuation of the light, which is calculatedusing the brightness value of the transmitted light image, and thisaspect is different from the fake finger determination apparatus of thefirst embodiment, which determines the authenticity of theauthentication target depending on the brightness value of thetransmitted light image.

The difference of the fake finger determination apparatus of the secondembodiment from the above mentioned fake finger determination apparatusof the first embodiment lies in the function of the determining unit 51of the controller 50. The other configuration is the same as that of thefake finger determination apparatus of the first embodiment, thereforeeach composing element is denoted with the same reference symbol forwhich description is omitted. In this section, the difference from thefirst embodiment will be mainly described.

The determining unit 51 calculates an attenuation factor to indicate adegree of attenuation of the light, using the brightness values of aplurality of predetermined pixels included in the transmitted lightimage captured by the imaging device 40, and determines the authenticityof the authentication target T depending on whether the attenuationfactor is within a predetermined range.

For the plurality of predetermined pixels, pixels can be set at apredetermined interval, from a location close to the light source 30 toa position distant from the light source 30, for example. A number ofthe predetermined pixels can be set to an efficient value consideringthe calculation according to the attenuation factor and the calculationtime of the attenuation factor.

For the predetermined range, a range of the attenuation factors which ahuman finger, imaged as the authentication target, could have, can beused.

The determining unit 51 can calculate the attenuation factor as follows.For example, the determination unit 51 obtains the brightness values atpoint A, point B and point C shown in FIG. 9 respectively, determinesthe inclination of the brightness values of these three points, andcalculates this inclination as the attenuation factor. For the methodfor determining the inclination, the least square method, for example,can be used. In this case, the determining unit 51 determines theinclination of the brightness values by determining the inclination ofthe line which minimizes least square errors.

The determining unit 51 may determine a coefficient a of the followingExpression 1, and calculate the coefficient a as the attenuation factor.Here x of Expression 1 is a distance from the light source, f(x) is afunction to indicate a brightness value of a pixel of which distancefrom the light source is x, and a is an attenuation factor.

f(x)=exp(−ax)  Expression 1

By determining the authenticity of the authentication object T using theattenuation factor, an imaging device with an automatic sensitivitycontrol function can be used for the imaging device 40. If the automaticsensitivity control function is included, however, the brightness valueof the image is corrected according to the sensitivity, and thebrightness value changes from the original value. Therefore thisfunction cannot be used for the fake finger determination apparatus 1 ofthe first embodiment, which determines the authenticity of theauthentication target within the range of the brightness values.

Whereas in the fake finger determination apparatus 1 of the secondembodiment, the authenticity of the authentication target is determinedusing an attenuation factor which is not changed by the automaticsensitivity control function. Therefore even if the brightness valuesare corrected by the automatic sensitivity control function, theauthenticity determination result of the authentication target is notaffected. Therefore the fake finger determination apparatus 1 of thesecond embodiment can not only have the above mentioned effects of thefirst embodiment, but can also be applied to an imaging device havingthe automatic sensitivity control function.

Third Embodiment

According to the above mentioned fake finger determination apparatus 1of the first embodiment, the light source 30 is disposed outside thedetermination target area, which is defined by the transparent plate 20(see FIG. 1 and FIG. 2). In this case, if the size of the thin film Mwith a forged fingerprint is set to the size of the transparent plate 20(determination target area), and the authentication target T is mountedand imaged in such a way that the thin film M is matched with the frameof the transparent plate 20, then the light of the light source 30 doesnot enter the thin film M, and enters only the human finger F. In thiscase, it becomes difficult to distinguish this brightness value of thetransmitted light image from the brightness value of the transmittedlight image generated when only the human finger F is imaged, andillegal acts can no longer be prevented.

According to the fake finger determination apparatus of the thirdembodiment, the light source 30 is disposed in a position surrounded bythe determination target area, and the authentication target T is imageda plurality of times while shifting the mounting position of theauthentication target T each time. Thereby it becomes possible to allowthe light source 30 to enter the thin film M at least once duringimaging, and illegal acts using thin film M matching with the size ofthe determination target area can be prevented.

The difference of the configuration of the fake finger determinationapparatus of the third embodiment from the above mentioned fake fingerdetermination apparatus of the first embodiment is that the transparentplate is divided into two, and the light source is disposed between thetransparent plates, and a combining unit 52 is added to the controller50. The other configuration is the same as that of the fake fingerdetermination apparatus of the first embodiment, therefore eachcomposing element is denoted with the same reference symbol for whichdescription is omitted. In this section, the difference from the firstembodiment will be mainly described.

The configuration of the fake finger determination apparatus accordingto the third embodiment will now be described with reference to FIG. 10and FIG. 11. FIG. 10 is a plan view depicting the fake fingerdetermination apparatus viewed from directly above. FIG. 11 is across-sectional view sectioned at XI-XI in FIG. 10.

The fake finger determination apparatus 1 has two transparent plates 20a and 20 b, and three light sources 30 a, 30 b and 30 c. The lightsources 30 a, 30 b and 30 c are disposed between the transparent plates20 a and 20 b. In other words, the light sources 30 a, 30 b and 30 c areinterposed in the determination target area which is formed connectingthe two transparent plates 20 a and 20 b. A number of transparent platesand a number of light sources can be freely set.

The transparent plates 20 a and 20 b and the light sources 30 a, 30 band 30 c are disposed so that the top faces thereof are located on thesame plane as the mounting surface. A mounting area P, to mount theauthentication target T, is created on the top faces of the transparentplates 20 a and 20 b and the light sources 30 a, 30 b and 30 c.

According to the fake finger determination apparatus 1 of the thirdembodiment, the mounting area P is created on two different locations onthe mounting surface. One is a first mounting area P1 illustrated inFIG. 12, and the other is a second mounting area P2 illustrated in FIG.13. A number of locations to create a mounting area is not limited totwo, but a mounting area can be created at arbitrary locations.

It is preferable that the positional shift between the first mountingarea P1 and the second mounting area P2 is set so as to match with thedistance between the transparent plates 20 a and 20 b. Then when theimages are combined as described later, an area which cannot be imagedbetween the transparent plates 20 a and 20 b can be interpolated by twoimages, and a combined image without any lost data can be generated.

The imaging device 40 captures images from inside the enclosure 10 inthe directions toward the transparent plates 20 a and 20 b. In otherwords, the imaging device 40 images the authentication target T mountedon the first mounting area P1 and the second mounting area P2 by way ofthe transparent plates 20 a and 20 b. Out of the transmitted lightimages captured by the imaging device 40, the portions in the respectiveframes of the transparent plates 20 a and 20 b are images used fordetermining the authenticity of the authentication target T disposed onthe first mounting area P1 and the second mounting area P2. In otherwords, the transparent plates 20 a and 20 b define the determinationtarget area to determine whether the authentication target T is a fakefinger.

It is preferable to set the imaging interval of the imaging device 40 toa time at least sufficient to change the mounting position of theauthentication target T and a time that makes it difficult to replacethe thin film M.

The combining unit 52 combines a plurality of transmitted light imagescaptured by the imaging device 40. This will be described in concreteterms with reference to FIG. 14. The combining unit 52 compares thepattern of the transmitted light images 11 a and 11 b of theauthentication target T mounted on the first mounting area P1 and thepattern of the transmitted light images 12 a and 12 b of theauthentication target T mounted on the second mounting area P2, forexample, and superposes similar characteristic points with each other soas to combine the transmitted light images 11 a and 11 b and thetransmitted light images 12 a and 12 b. Thereby the combined image ofthe authentication target T can be generated.

If the similarity between the patterns is lower than a predeterminedthreshold, the combining unit 52 outputs an input error, and prompts forre-input of the authentication target T. If illegal acts of replacing athin film M to match the transparent plate are performed each time themounting position of the authentication target T is changed and imaged,similarity between the patterns becomes low, therefore theauthentication target T can be rejected as an input error.

The determining unit 51 determines the authenticity of theauthentication target using the brightness value of the image combinedby the combining unit 52. For the method of determining the authenticityof the authentication target, various methods described in the firstembodiment and the second embodiment can be used.

For example, the determining unit 51 can determine the authenticity ofthe authentication target depending on whether the brightness value ofthe predetermined pixel included in the combining image combined by thecombining unit 52 is within a predetermined range.

The determining unit 51 can also determine the authenticity of theauthentication target by calculating the attenuation factor to indicatea degree of authentication of light using the brightness values of aplurality of predetermined pixels included in the combined imagecombined by the combining unit 52, and determining whether thisattenuation factor is within a predetermined range.

As described above, according to the fake finger determination apparatus1 of the third embodiment, the light sources 30 are disposed in thedetermination target area, and the authentication target T can be imageda plurality of times while shifting the mounting position thereof.Therefore even if a fake finger on which a thin film M, matching thesize of the determination target area, is attached is used, the light ofthe light sources 30 can enter the thin film M with certainty. As aresult, illegal acts using a thin film M matching the size of thedetermination target area can be prevented.

Each embodiment mentioned above is merely an example, and does notnegate various modifications and the use of technologies not explicitlystated in an embodiment. In other words, the present invention can bemodified in various forms within the scope not departing from the truespirit of the invention.

For example, in each embodiment mentioned above, the determinationtarget area is defined by a transparent plate, but the means of definingthe determination target area is not limited to a transparent plate. Anyother means can be used as long as the means can define an image to beused for determining the authenticity of the authentication targetmounted on the mounting area.

The fake finger determination apparatus according to each embodimentmentioned above has each composing element illustrated in FIG. 1, oreach composing element illustrated in FIG. 11, but the fake fingerdetermination apparatus does not always require all of these composingelements. For example, the fake finger determination apparatus 1 canhave at least the enclosure 10, the transparent plate 20, the lightsource 30 and the imaging device 40, as illustrated in FIG. 15. In thiscase, the determining unit 51 and the combining unit 52 of thecontroller 50 can be separately connected outside the fake fingerdetermination apparatus 1.

This application declares a priority based on Japanese PatentApplication No. 2009-245298 applied on Oct. 26, 2009, and includes theentire disclosure thereof.

Although the present invention has been described with reference to theembodiments, the present invention is not limited to the embodiments.The configuration and details of a present invention can be modified innumerous ways by those skilled in the art without departing from thescope of the invention.

The fake finger determination apparatus and the fake fingerdetermination method according to the present invention are suitable forimproving accuracy to discern a fake finger created by attaching atransparent film to the surface of a finger.

-   1 fake finger determination apparatus-   10 enclosure-   20 transparent plate-   30 light source-   40 imaging device-   50 controller-   51 determining unit-   52 combining unit

1-10. (canceled)
 11. A fake finger determination apparatus comprising: amounting surface that has a mounting area to mount an authenticationtarget that is an object of fingerprint authentication; an imaging unitthat is provided on the mounting surface and images the authenticationtarget mounted on the mounting area by way of an image capturing areathat defines a range of an image to be captured; one or a plurality oflight sources that allow light to directly enter the authenticationtarget mounted on the mounting area, not by way of the image capturingarea; and a determining unit that determines the authenticity of theauthentication target depending on whether a brightness value of one ora plurality of predetermined pixels included in the image captured bythe imaging unit is within a range of the brightness values which ahuman finger imaged as the authentication target could exhibit, inaccordance with a distance between the light source and the pixel,wherein a light emitting surface for emitting the light of the lightsource to outside is disposed on the same plane as the mounting surface.12. The fake finger determination apparatus according to claim 11,wherein the light emitting surface is disposed adjacent to the imagecapturing area.
 13. The fake finger determination apparatus according toclaim 11, wherein the emission surface is surrounded by the imagecapturing area, and the imaging unit captures images of theauthentication target, which is mounted on a plurality of mounting areasdisposed in different positions in the image capturing area.
 14. Thefake finger determination apparatus according to claim 13, furthercomprising: a combining unit that combines a plurality of imagescaptured by the imaging unit; and a determining unit that determines theauthenticity of the authentication target by using the brightness valueof the image combined by the combining unit.
 15. The fake fingerdetermination apparatus according to claim 14, wherein the determiningunit determines the authenticity of the authentication target dependingon whether a brightness value of one or a plurality of pixels includedin the image combined by the combining unit is within a range of thebrightness values which the human finger imaged as the authenticationtarget could exhibit.
 16. The fake finger determination apparatusaccording to claim 14, wherein the determining unit calculates anattenuation factor indicating a degree of attenuation of light by usinga brightness value of a plurality of predetermined pixels included in animage combined by the combining unit, and determines the authenticity ofthe authentication target depending on whether the attenuation factor iswithin a range of attenuation factors which a human finger imaged as theauthentication target could exhibit.
 17. A fake finger determinationmethod comprising steps of: mounting an authentication target that is anobject of fingerprint authentication on a mounting surface that has amounting area to mount the authentication target; allowing light from alight source to directly enter the authentication target mounted on themounting area, not by way of an image capturing area that is provided onthe mounting surface and defines a range of an image to be captured;imaging the authentication target mounted on the mounting surface byusing an imaging unit by way of the image capturing area; anddetermining the authenticity of the authentication target depending onwhether a brightness value of one or a plurality of predetermined pixelsincluded in the image captured by the imaging unit is within a range ofthe brightness values which a human finger imaged as the authenticationtarget could exhibit, in accordance with a distance between the lightsource and the predetermined pixel, wherein a light emitting surface foremitting the light of the light source to outside is disposed on thesame plane as the mounting surface.